1. Field of the Invention
The present invention relates to a concentrate composition for forming an aqueous foam. Specifically, the present invention concerns a concentrate composition suitable for use in forming stable, economical aqueous foams which foams are suitable for use as fire suppressant foams particularly fire suppressant foams for use in fighting wildland fires.
In the past, it has been known to use aqueous foams for a variety of purposes. Such foams have been used in security systems, as foam drilling fluids for deep well drilling and as fire fighting agents. Other uses for aqueous foams are apparent to those skilled in the art.
In a relatively recent innovation, aqueous foams have proven extremely effective in combating forest fires. Typically, such aqueous foams are formed by discharging a water/foaming agent mixture from a water scooping aircraft flying above the site of the forest fire. The water/foaming agent mixture "flash foams" upon discharge from the plane and falls onto the forest fire. For ground use applications the water/foaming agent mixture is foamed by passing it through an air aspirating nozzle or by employing an air injection delivery system known as a WEP's system to those skilled in the art. The foams function in much the same way as water, that is, they serve to "wet" the fuel. Unlike water, the aqueous foams coat the fuel (trees, etc.) thus keeping the water where it will best penetrate into the fuel. As can be understood by the described process, converting water into an aqueous foam allows a greater fire suppressant activity to be achieved from a given amount of water than if said water were applied directly to the fire. This is achieved through the increased surface area of the water due to the foaming process.
Foams possessing slower drain rates are generally better wildland fire suppressants since they hold the water up in the fuel for longer periods of time. The drainage rate of foams is directly related to the expansion ratio of the foams. An increase in the expansion ratio results in a slower drainage rate. However, the higher the expansion ratio the less water is actually present in a given volume of foam. Finally, drainage rate is inversely proportional to the square of the size of the foam bubbles. As can be appreciated from the above, the effectiveness of a particular foam is dependent on a variety of factors including bubble size, expansion ratio, water content, and drainage rate.
A major problem in combating forest fires is transporting water to the site of the fire. The use of an aqueous foam which provides a greater amount of fire suppressant activity to be developed from a given amount of water is, therefore, highly desirable.
Additionally, the use of aqueous foams in combating forest fires has the advantage that such foams impact relatively gently upon the vegetation to which they are applied as compared to the impact water causes when dropped from a source such as an airplane. Additionally, the use of aqueous foams allows the water present therein to cling to vegetation and resist run off into the soil, thereby increasing the fire suppressant activity of the water present therein.
Aqueous foams suitable for use in combating fires are known in the art. Exemplary of such foams are the foams described in U.S. Pat. No. 3,186,943 issued June 1, 1965 to Barthauer. Barthauer claims a method of generating a fire extinguishing foam from a concentrate which concentrate consists essentially of the ammonium alkyl ether sulfate of about 4 moles of ethylene oxide with 1 mole of C.sub.10 to C.sub.20 aliphatic fatty alcohol and an aliphatic fatty alcohol selected from the class consisting of lauryl alcohol and myristyl alcohol in an amount of up to 12 and one-half percent by weight of said sulfate.
U.S. Pat. No 4,442,018 issued Apr. 10, 1984 to Rand, describes a stabilized aqueous foam system and concentrate and method for making them. Rand discloses a foam concentrate comprising a combination of a water soluble polymer of the polyacrylic acid type, a foam stabilizer of dodecyl alcohol, a surfactant, a solvent and water.
As indicated by the two cited U.S. Patents, the use of concentrates in forming aqueous foams for use in fire fighting applications are known. Nonetheless, prior art concentrates and foams formed therefrom have demonstrated certain undesirable qualities. For example, the foam concentrates described by Barthauer and Rand are unsatisfactory in that they contain flammable solvents which lower the flash points of the concentrates themselves thus making them more difficult to use safely. Additionally, the concentrates are not concentrated enough to render them suitable for use in wildland fire fighting since they need to be added to water in amounts which are too high to allow economical use.
The concentrates described by Rand have proven undesirable in that they are added to water at levels of 6-10 percent. These levels also render said concentrates unacceptable for use in fighting wildland fires. Moreover, the concentrates of Rand are somewhat difficult to mix into water, a characteristic which also makes them unsuitable for use in fighting wildland fires.